This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-290727, filed Sep. 25, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device-manufacturing method, particularly to a heat-radiating step.
2. Description of the Related Art
Usually, a semiconductor device-manufacturing method includes a die-mount step and a connection step. In the former step semiconductor elements are die-mounted on lead frames, and in the latter step the electrodes of the semiconductor elements and lead frames are connected through metal wires.
FIG. 8 illustrates the outline of a semiconductor device-manufacturing method wherein the die-mount step mentioned above is a solder vapor-depositing step. In this method, solder 51 is vapor-deposited on the reverse side 52a of a semiconductor conductor wafer 52 in order to form unseparated semiconductor elements 53. The semiconductor elements 53 are separated by dicing the semiconductor conductor wafer 52 along predetermined lines. Then, the semiconductor elements 53 are mounted on lead frames 54, and the electrodes of the semiconductor elements and the lead frame 54 are connected through metal wires 55, thereby fabricating semiconductor devices 56.
FIG. 9 illustrates the outline of the semiconductor device-manufacturing method wherein the die-mount step mentioned above is a solder pre-coat step. In this method, fused solder 51 is supplied onto lead frames 54, and semiconductor elements 53 formed by dicing the semiconductor conductor wafer 52 are scrub-mounted on the fused solder 51. Then, the connection step is carried out to connects the electrodes of the semiconductor elements 53 to the lead frames 54 by means of metal wires 55, thus fabricating semiconductor devices 56. The xe2x80x9cscrub-mountingxe2x80x9d is intended to refer to an operation of scrubbing the semiconductor elements 53 and the lead frames 54 against each other in such a manner as to spread the fused solder 51, for joining.
The semiconductor device-manufacturing methods described above have the following problems. That is, when wire bonding is utilized, a semiconductor element is first die-mounted on a lead frame, and then a metal wire is connected to the lead frame. Because of this procedure, the metal wire forms a loop in the region surrounding the semiconductor element, and a dead area is inevitably produced. To be more specific, the land the lead frame has for connection has to be spaced from the semiconductor element more than a predetermined distance. In addition, since the loop is formed from the terminal, a margin corresponding to the height of the loop is needed. As can be seen from this, the conventional methods impose restrictions on the miniaturization of semiconductor devices.
As a method of connecting a lead frame and a semiconductor element without using a wire, connection by flip chip bonding is proposed. In flip chip bonding, bumps are formed on the bonding pads of a semiconductor element, for alignment with the lead frame, and the solder reflow based on the application of heat or ultrasonic vibration executed in a pressure-applied state is utilized for connection.
The manner in which solder is supplied in the die-mount step will be considered. Where the die-mount step is the solder vapor-depositing step, a long time is required for supplying the solder to the reverse side of a semiconductor element. On the other hand, where the die-mount step is the solder pre-coat step, the fused solder cannot be supplied at high speed.
A semiconductor device manufactured in the manufacturing methods described above will be looked at in light of thermal design. Even if a semiconductor device is provided with a heat sink (metal plate) 61, this heat sink 61 is within those portions of sealing resin 62 which are located near a semiconductor element 53, as shown in FIG. 10. With this structure, heat is radiated mainly to a substrate 63 after passing by way of the lead frame 54 and the sealing resin 62, as indicated by arrows xe2x80x9cHxe2x80x9d in FIG. 10. It is therefore impossible to expect a high heat radiation efficiency.
Recently-developed semiconductor elements are highly integrated and operate at high speed, and therefore generate a large amount of heat. In addition, they have to be arranged at high density since recent electronic devices are very small. As long as the heat sink is embedded within the sealing resin, the semiconductor element may not maintain a normal operating temperature (which depends upon the type of semiconductor element and is normally lower than 80xc2x0 C. or so), adversely affecting the reliability of the semiconductor element.
Accordingly, an object of the present invention is to provide semiconductor device-manufacturing method for manufacturing semiconductor devices which are approximately the same in size as semiconductor elements and which have an improved heat radiating efficiency.
To solve the problems and to attain the object, the present invention provides semiconductor device-manufacturing methods described below.
A semiconductor device-manufacturing method comprising: a laminated wafer formation step of placing a semiconductor wafer in such a manner that a side having no electrode and no electronic circuit faces a solder material, then laying a metal plate on that side of the semiconductor wafer with a solder material interposed, and then causing the metal plate and the wafer to form a one-piece structure by decompression pressing, thereby obtaining a laminated wafer; and a dicing step of dicing the laminated wafer to form laminated chips.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.